In English, "equal" is both an adjective and a verb. So this is correct. But you can't take an arbitrary verb and use it as an adjective, or an arbitrary adjective and use it as a verb. There are other examples where the same word is used in different parts of speech. For instance the word "smile" is both a noun and a verb. But each word is different, so you have to learn each word individually and learn how it can be used. Most words can only be used in one part of speech.